IGF-I and mammographic density in four locations: A pooled analysis.

B186

Insulin-like growth factor (IGF-I) and prolactin have been found to be associated with breast cancer risk and with mammographic density, a strong predictor of breast cancer risk. In a pooled analysis from four locations, we investigated the association of percent mammographic densities with IGF-I, its binding protein IGFBP-3, and prolactin in populations at different breast cancer risk. After combining data from each location, this analysis included 1,327 pre- and postmenopausal women: Caucasians from Norway, Arizona, and Hawaii, Japanese from Hawaii and Japan, Latina from Arizona, and Native Hawaiians from Hawaii. Serum samples were assayed for IGF-I, IGFBP-3, and prolactin levels using ELISA assays. Mammographic density was quantified using a computer-assisted density method. After stratification by menopausal status, multiple regression models estimated the relation between serum analytes and breast density and computed covariate-adjusted mean serum analyte levels by ethnicity and location. All serum analytes except IGFBP-3 among postmenopausal women differed significantly by group. Among premenopausal subjects, IGF-I levels and the molar ratio were highest in Hawaii, intermediate in Japan, and lowest in Arizona. For IGFBP-3, the order was reversed. Among postmenopausal women, Caucasians in Norway had the highest IGF-I levels, followed by women in Hawaii, Japan, and Arizona. We observed no significant relation between percent density and IGF-I or prolactin levels among pre-and postmenopausal women. Our study indicated that the influence of IGF-I, IGFBP-3, and prolactin on percent density is relatively small.The significant differences in IGF-I levels by location but not ethnicity suggest that environmental influences determine IGF-I levels, while breast density has a stronger association with ethnicity.